STUDIES IN THE EXPERIMENTAL ANALYSIS OF SEX. 293 
ment and sign of more deep-seated changes, which may 
involve perhaps several kinds of side-chains attached to 
proteid-molecules or cast loose in the blood. 
Another question which must be left to the future to 
decide is, what may be the corresponding action exerted by 
the testis of the male upon the metabolism and on the 
composition of the blood, what food-particles is it seizing on, 
and of what side-chains or linkages is it stimulating the 
formation ? For answering these questions we have at 
present little or no data. 
We are now in a position to explain how the theory put 
forward above differs from and is superior to the Hormone 
theory of sexual development as held by the great majority 
of physiologists. It is clear that both theories may be 
legitimately described as internal secretion ” theories as 
long as we leave the mode of production and of action of 
the internal secretion entirely vague, but if we pay attention 
to those two not unimportant considerations, we find that the 
account given of them by the two theories is entirely different, 
and I submit that the account given by the Hormone theory 
is erroneous and not supported in fact. 
According to the Hormone theory, the Gonad produces an 
internal secretion or hormone which it pours into the blood, 
and which stimulates the appropriate secondary sexual 
characters to develop. The method by which its adherents 
attempt to prove this theory is by injecting extracts of the 
Gonad which contains this substance in the hope that the 
development of the appropriate secondary sexual characters 
will be called forth. Partly by judging from the analogy 
of other cases, and partly by trusting the specious results of 
experiments designed to prove the case, it is not too much to 
say that the majority of physiologists and zoologists believe 
that the Hormone theory is experimentally proved for the 
reproductive organs. Whilst admitting that these experiments 
should receive careful consideration and repetition — especially 
the latter — I cannot agree that they are in any case conclusive, 
while sources of error exist as far-reaching and as difficult of 
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